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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Direct Observation of Intracavity Pulse Dynamics in All-Normal Dispersion All-Fiber Oscillator
摘要： Ultrafast science and technology depend strongly on the development of novel ultrafast sources, thus good understanding of nonlinear phenomena in such systems is of essence. In this paper, we present the experimental observation and theoretical analysis of various pulse dynamics in all-normal dispersion cavity producing dissipative soliton pulses. We report the results of an extensive study regarding the Stimulated Raman Scattering (SRS) process, which creates a main upper limitation for the pulse energy achievable from all-normal dispersion fiber oscillators. We report the measurements of real-time, single shot spectra registered using Dispersive Fourier Transform (DFT) technique together with measured averaged spectral phase of the pulses generated from an all-PM-fiber oscillator mode-locked with Nonlinear Optical Loop Mirror (NOLM). It is found that NOLM parameters directly influenced the pulse stability and dynamics. The Yb-doped fiber was used as an active medium and Dissipative Soliton (DS) pulses centered at 1030 nm were generated together with Stokes radiation shifted by 440 cm-1 (centered approximately at 1078 nm) produced in SRS process. The light generated in SRS process was suppressed from round-trip to round-trip by a narrow pass-band spectral filter centered at 1030 nm placed inside the laser cavity. We present the broad experimental study of ultrashort pulse dynamics with strong presence of SRS process. Spectral intensity correlation maps were calculated to describe how the SRS process disturbs the ultrashort pulse during propagation in the cavity (Fig. 1). The intensities of longer wavelengths (1040 – 1050 nm) in the pulse spectrum were destabilized due to the SRS process. In normal dispersion fiber Stokes SRS components have higher group velocity than the pulse spectral components. For positively chirped pulse SRS affects only the leading edge of the pulse which is manifested as negative correlation (Fig. 1(c)). The phenomena of repetitive partial dissipative soliton explosions and bistability of the pulse operation in an all-PM-fiber all-normal dispersion oscillator cavity were investigated as well. The clear signature of bistable operation was the hysteresis of the laser pulse power versus input pump power. Furthermore, we registered significant differences between the measured pulses spectral phases for each case. Another set of measurements was performed to analyze the pulse self-starting dynamics. We present the experimental study and numerical simulations of DS pulse dynamics in an all-normal dispersion all-fiber cavity. The numerical simulations were performed using the standard split-step Fourier-transform method employing the multi-vibrational model of SRS. DS lasers are important pulse sources and an effective platform to investigate the pulse dynamics and nonlinear processes inside the all-fiber cavities.
关键词： spectral intensity correlation maps,Yb-doped fiber,dissipative soliton pulses,Dispersive Fourier Transform,split-step Fourier-transform method,Nonlinear Optical Loop Mirror,Stimulated Raman Scattering,ultrafast science
更新于2025-09-12 10:27:22
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Nonlinear Optical Properties of Zinc Oxide Thin Films Produced by Pulsed Laser Deposition
摘要： In this work, the nonlinear optical properties of Zinc Oxide (ZnO) thin films produced on microscope slide glass substrates at room temperature (RT) using Pulsed Laser Deposition (PLD) method has been presented. PLD system consists of a vacuum chamber (pumped by a turbo molecular pump, backed with a rotary pump), rotating sample and substrate holders, optical thickness measurement system, infrared temperature measurement system and a nanosecond laser system. Previously deposition vacuum chamber evacuated down to ~10-8 mbar and deposition was taken place about 1.3×10-1 mbar oxygen background gas pressure value. Morphological properties of thin films were obtained by Atomic Force Microscopy (AFM) that shows homogenous and smooth film structure. Thin films crystallinity were investigated by using X-Ray Diffraction (XRD) method and showed that polycrystalline ZnO structure with the largest peak corresponding to (002) orientation but some films contain Zn with (101) orientation . The thicknesses of the films were deduced from reflectance measurement using a fitting software and crosschecked with profilometer and AFM measurements. The thickness of the films ranged between 10 nm and 220 nm. Linear optical properties were obtained by using UV-VIS Spectrometer. Furthermore, we presented the nonlinear optical properties of the ZnO thin films that were obtained by the z-scan method.
关键词： Z-scan system,Zinc Oxide Thin Film,Nonlinear Optical Properties,Pulsed Laser Deposition
更新于2025-09-12 10:27:22
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Quantum-enhanced tunable spin-valley dependent excitonic second harmonic generation in molybdenum disulfide quantum dots
摘要： Developing a robust system with a strong tunable nonlinear second harmonic generation (SHG) is desirable. In this work, we calculate SHG arising from the excitonic states of monolayer molybdenum disulfide quantum dots (MoS2 QDs) with a parabolic confinement potential within massive Dirac fermion model using the density matrix formalism. We theoretically demonstrate that MoS2 QDs can exhibit a giant and tunable Spin-Valley dependent excitonic SHG, which can be tuned from 0 to ～107 pm/V and realized by biasing nanostructured gates or by position-dependent doping. Remarkably, the strength of SHG response is more than two orders of magnitude higher than that in monolayer MoS2. Furthermore, robust excitonic effects together with strong spin-valley coupling in monolayer transition metal dichalcogenides quantum dots (TMDC QDs), which are tunable depending on the strength of the quantum confinement, make them as a promising candidate for ultrathin nonlinear optical materials with large nonlinearities. We believe that this study could spark interest in the nonlinear optical properties of TMDC QDs and open up a variety of new avenues for versatile novel 2D nonlinear photonics and optoelectronic nanodevices.
关键词： second harmonic generation,spin-valley coupling,TMDC QDs,excitonic nonlinear optical properties
更新于2025-09-12 10:27:22
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Frequency-Multiplexed Photon Pairs Over 1000 Modes from a Quadratic Nonlinear Optical Waveguide Resonator with a Singly Resonant Configuration
摘要： We demonstrate a frequency multiplexed photon pair generation based on a quadratic nonlinear optical waveguide inside a cavity which confines only signal photons without confining idler photons and the pump light. We monolithically constructed the photon pair generator by a periodically poled lithium niobate (PPLN) waveguide with a high reflective coating for the signal photons around 1600 nm and with antireflective coatings for the idler photons around 1520 nm and the pump light at 780 nm at the end faces of the PPLN waveguide. We observed a comblike photon pair generation with a mode spacing of the free spectral range of the cavity. Unlike the conventional multiple resonant photon pair generation experiments, the photon pair generation was incessant within a range of 80 nm without missing teeth due to a mismatch of the energy conservation and the cavity resonance condition of the photons, resulting in over 1000-mode frequency multiplexed photon pairs in this range.
关键词： frequency multiplexed photon pair generation,photon pair generator,PPLN waveguide,quadratic nonlinear optical waveguide,singly resonant configuration
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Development of Figure-8 Variable Pulse Width Fiber Laser using Coherent Resonator Coupling Technology
摘要： A femtosecond pulsed laser has an extremely short pulse width and high peak power and is used for the field of microfabrication. On the other hand, laser cutting and drilling requires picosecond pulsed laser with high pulse energy. In general, a diffraction grating or a band pass filter is used to control pulse width. However, these components are not affordable and the optical system with them becomes complicated. Therefore, we have developed all fiber variable pulse width laser by applying a coherent resonator coupling technology that increases the output power by coupling the phases of longitudinal modes generated by sharing an output coupler in multiple laser resonators. In the coherent resonator coupling, resonator length difference decreases coupled longitudinal modes and narrows spectral width (?ν). Thus, pulse width (?t) is widened according to equation (1). ?t ? ?ν = const (1) We will describe the configuration of the resonator used in the experiment. A resonator coupling technology is applied to a figure-8 fiber laser. The figure-8 fiber laser is a ring resonator that contains a nonlinear optical loop mirror. It operates as a resonator only when a phase difference occurs between the clockwise light that travels through the loop of the mirror and the counter-clockwise one. The phenomenon functions as a saturable absorption effect and generates femtosecond pulses. Further, we use a variable delay line in one of the resonator to control resonator length difference. Figure 1 shows the configuration of the figure-8 variable pulse width fiber laser and Fig. 2 shows the configuration of a nonlinear optical loop mirror.
关键词： femtosecond pulsed laser,figure-8 fiber laser,picosecond pulsed laser,nonlinear optical loop mirror,coherent resonator coupling technology
更新于2025-09-12 10:27:22
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Photo-Switchable Boronic Acid Derived Salicylidenehydrazone Enabled by Photochromic Spirooxazine and Fulgide Moieties: Multiple Responses of Optical Absorption, Fluorescence Emission, and Quadratic Nonlinear Optics
摘要： A novel protocol of the boronic acid derived salicylidenehydrazone (BASHY) core being sandwiched by photochromic spirooxazine and fulgide moieties was proposed here to design multistate fluorescent photoswitches with variable nonlinear optical (NLO) responses. Systematic investigations on their optical absorption, fluorescence emission, and static first hyperpolarizabilities (β) were performed using density functional theory (DFT). It was found that the BASHY-based sandwiched series exhibited significant differences of absorption and emission properties between three photoisomers, which were essentially ascribed to the massive changes of corresponding electron transition characteristics quantified by hole–electron descriptors and visualized by electron density difference (EDD) plots. However, the isomerization of fulgide parts in the merocyanine (MC) form of spirooxazine failed to greatly shift maximum absorption/emission wavelengths, due to their high similarity of intrinsic transition features. Furthermore, large β contrasts between three photoisomers were observed, which resulted from significant variations of contributions of spirooxazine and/or fulgide moieties to the total β upon photoisomerization according to β densities. Although the fulgide moiety contributes negatively and positively to spirooxazine (SO) isomers when fulgide switches from close (C-) to open (E-) forms, respectively, their dominant βxxx values with opposite signs are still similar in magnitude, leading to quite close quadratic NLO responses. Therefore, the captivating ternary photoswitches with multiple responses of absorption, emission, and NLO were elaborately built in this context, promising to be applied as multifunctional optical materials in various scientific and technological fields.
关键词： photochromic spirooxazine,fulgide moieties,nonlinear optical (NLO) responses,density functional theory (DFT),boronic acid derived salicylidenehydrazone (BASHY)
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Topological Control of Optical Nonlinear Waves
摘要： Controlling nonlinear optical processes is a signi?cant challenge in photonics. Shock waves, rogue waves, and solitons are widespread, from optics to hydrodynamics. Intense research is dedicated to advanced techniques for tailoring extreme waves and ?nding the conditions to induce transitions from one kind of wave to another. We develop a new strategy to supervise, modify or tune a laser beam in third-order nonlinear materials, when light propagation is ruled by the nonlinear Schr¨odinger equation (NLSE). We denote our approach topological control (TC). TC is based on the one-to-one correspondence between the number of wave packet oscillating phases and the genus of toroidal surfaces associated with the NLSE solutions by the Riemann theta function [1]. For a box-shaped wave in a focusing Kerr medium, TC allows to control transitions from dispersive shock waves (DSWs), to rogue waves (RWs) and soliton gases (SGs). We prove that our method is experimentally realizable in a photorefractive crystal [2]. Speci?cally, we use the parametric time-dependence of photorefractive nonlinearity to shape the asymptotic wave pro?le. We tailor time-dependent propagation coef?cients, as nonlinearity and dispersion, to explore each region in the state-diagram [Fig. 1(a)] and observe all the phases in the nonlinear wave evolution [Fig. 1(b)]. This new technique casts light on focusing DSWs and RW generation, and can be extended to many other nonlinear phenomena, from classical to quantum ones.
关键词： photorefractive crystal,nonlinear Schr¨odinger equation,topological control,nonlinear optical processes,shock waves,rogue waves,solitons
更新于2025-09-11 14:15:04
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Applied Surface Science || Synthesis and Nonlinear Optical Studies on Organic Compounds in Laser-Deposited Films
摘要： Organic semiconductors as active materials in thin-film electronic devices such as alkynes, heterocycles, dyes, ferrocenes, spiranes, or porphyrins, with special geometries and certain electronic molecular parameters, which possess nonlinear optical (NLO) properties and offer several major advantages over their inorganic counterparts, are presented in this chapter. There are a number of simple and versatile techniques that can be employed for the deposition of these important classes of materials. The matrix-assisted pulsed laser evaporation (MAPLE) technique provides advantages with regard to making organic films of different morphologies on different types of substrates. New insights into the crystallization growth mechanisms in MAPLE-deposited conjugated polymer films, which realize the connection between the structure and the carrier transport properties, are discussed herein. Second harmonic generation (SHG) capabilities of the thin films were also investigated.
关键词： thin films,organic synthesis,nonlinear optical properties,laser deposition
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - High Energy Pulsed Operation of a Yb Fibre MOPA with Amplified Spontaneous Emission Output
摘要： High energy pulsed fibre lasers are attractive to numerous applications in areas including industry, science, metrology and defense due to their excellent characteristics such as high average powers, a diffraction-limited beam quality, compactness and high flexibility in operation. However, their pulse energy is often limited by nonlinear optical phenomena, such as SBS (Stimulated Brillouin Scattering), SRS (Stimulated Raman scattering), self-focusing, etc., due to the small core size, resulting in unstable operation and catastrophic damage of the fibre. Enlarging the core size along with shortening the fibre length is a simple and straightforward way to overcome this problem, but at the expense of beam quality degradation and increased thermal effects. Fibre-based superfluorescent sources (FSS), sometimes referred to as amplified-spontaneous-emission (ASE) fibre light sources, can be an alternative way to achieve higher pulse energy from a typical step-index fibre while preserving the good beam characteristics of the fibre laser. Since the FSS has a broad spectrum without longitudinal modes, its spectral power is smaller than that of the fibre laser, increasing SBS threshold and, hence, generation of a high energy pulse. In this study, we report pulsed operation of the fibre-based superfluorescent light source. From a Yb fibre MOPA using an ASE source as a seed, we successfully generated high energy superfluorescent light pulses and investigated its performance for different repetition rates, pulse widths, and spectral linewidths. Furthermore, the results were compared with those of a Yb fibre laser.
关键词： ASE fibre light sources,self-focusing,fibre-based superfluorescent sources,nonlinear optical phenomena,amplified spontaneous emission,SBS,SRS,Yb fibre MOPA,High energy pulsed fibre lasers
更新于2025-09-11 14:15:04
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Structural, Spectroscopic, and Excitonic Dynamic Characterization in Atomically Thin Yb <sup>3+</sup> ‐Doped MoS <sub/>2</sub> , Fabricated by Femtosecond Pulsed Laser Deposition
摘要： The large area deposition and synthesis of 10 mm × 10 mm atomically thin Yb3+-doped MoS2 films by femtosecond pulsed laser deposition on a silica glass optical platform for device applications are demonstrated for the first time. The presence of Yb3+-ion doping is confirmed using photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The Yb3+-doped MoS2 films, when excited with a 976 nm laser, exhibit room temperature PL with a peak at 1002 nm. The XPS and Raman spectroscopic analyses of the Yb3+-doped and undoped films show that the deposited films are a mixture of 2H- and 1T-MoS2 after postdeposition annealing at 500 °C. The density functional theory analysis shows that the 1T phase is metastable by +77 kJ (≈0.8 eV) mol-1, when compared with the 2H state at 0 K. Ultrafast transient nonlinear optical spectroscopic measurements prove that the saturable absorption of undoped MoS2 is significantly modified after Yb3+-ion doping, by displaying dopant-host structure charge transfer. The complex transient absorption line shape shows a combination of bleach (negative) signals at the A (670 nm) and B (630 nm) exciton energies, and a strong induced absorption below the A exciton level. The results presented herein provide critical insight in designing novel rare-earth-ion doped 2D materials and devices.
关键词： molybdenum disulfide,femtosecond pulsed laser deposition,saturable absorber,rare-earth ion photoluminescence,nonlinear optical properties
更新于2025-09-11 14:15:04